It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) passed by a dead sheep and he (peace and blessings be upon him) said: "Why did you not benefit from its skin?" They said: But it is a carcass? He (peace and blessings be upon him) said: "Only eating it is forbidden." Aqil added these words: "Is there not in water and acacia bark what would purify it?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 64